According to the researchers, more than half of household water is used to water the garden, flush the toilet or wash clothes, situations where some people say drinking-quality water is not needed.

So, six years into a drought and with water restrictions in place, Australians are turning to alternative sources of water for these needs.

"Because of the drought and long-term climate change we are looking at using different water sources to substitute for what we currently use drinking quality water for," one of the authors, Dr Martha Sinclair, told ABC Science Online.

Faecal contamination is one issue with using recycled greywater, which comes from washing machines and showers, Sinclair said.

"It depends who is living in the house. Of course if you are washing nappies and so forth you will have a substantial amount [of faecal matter]."

Faecal matter can form a breeding ground for pathogenic bacteria and together with soaps and body fats washed off in showers can form scum. That makes it "smelly and objectionable, quite apart from the health risks", Sinclair said.

Not many people were using greywater in Australia so far, Sinclair said. But she predicted the current water shortages would increase its use.

For example, water pipes for recycled water were being installed in some new housing developments, Sinclair said.

"There are potential issues there. Even if you warn people not to use water for certain purposes there is a chance they will forget, or use recycled water because it is cheaper than drinking-quality water," she said.

People renovating houses with recycled-water pipes could also be at risk, she said, as they could accidentally connect the wrong pipes so recycled water ends up as drinking water.

She cited reports of people in the Sydney suburb of Rouse Hill who used recycled water to fill their swimming pools because it was cheaper than drinking-quality water. She said there were risks associated with this as kids occasionally swallowed the water.

Advice on using recycled water

Sinclair is working on new government guidelines that address alternative water sources.